The objective of this research proposal is the study of the ontogeny of dopamine receptors and neuroleptic receptors in the rat brain. This will be carried out using radiolabeled spiperone, a neuroleptic drug with a high affinity for the dopamine receptor and a very slow dissociation rate. The initial pharmacological studies will determine the best route of administration of this drug for labelling dopamine receptors in vivo in neonatal rat. The time course of specific spiperone binding will be studied as well as its regional distribution, saturability, pharmacological profile and the metabolism of 3H-spiperone in neonatal brain. These pharmacological studies will provide the best conditions for in vivo labelling of dopamine and neuroleptic receptors in neonatal rat brain analogous to studies already completed in the adult and they will be the basis for autoradiographic studies of the development of these receptors. The establishment of the autoradiographic technique as on-going in the principal investigator's laboratory is one of the principal purposes of this proposal. Following the establishment of this technique, this high resolution approach will be used to describe the development of dopamine receptors in the brain of the rat from day 5 to day 30 after birth and to correlate what is found at the light microscopic level with previous biochemical, pharmacological and histological studies.